This competitive renewal application is designed to test two hypotheses about the molecular mechanisms responsible for hearing loss (HL) in human and role of inositol pyrophosphates in the inner ear sensory cells development and function. These studies will use human genetics, zebrafish and mouse models to specifically test these hypotheses. HL is a highly variable phenotype that affects over 70 million children worldwide. Genetic and functional studies of the HL associated proteins have helped elucidate the molecular components of inner ear tissue, but the molecular identities of many essential components of inner ear sensory cells are still unknown. The long-term goals of the proposed research are to elucidate molecular networks essential for the development and function of mammalian inner ear, to help decipher mediating mechanisms and develop new therapeutic agents for its treatment and prevention. The objectives of this particular application are to identify and/or characterize 4 new molecular determinants of HL and characterize their functions using zebrafish and mouse models. The rationale for the proposed research is that identifying a causative gene and understanding its normal function is essential for preventing hearing and for the development of therapeutic agents to treat HL. Thus, the proposed research is relevant to that part of NIH?s mission that pertains to developing fundamental knowledge that will potentially help to reduce the burdens of human disability. In our preliminary data we have already identified the 2 new HL genes: DFNB100, and DFNBX, and have mapped the chromosomal positions of 2 additional genes (DFNBY & DFNBZ) essential for auditory function. Also, our preliminary studies revealed progressive HL and hair cells degeneration in the Dfnb100 mouse model. Our two specific aims will: (1) identify and functionally characterize all 4 deafness gene; (2) determine the mechanism of inositol pyrophastase associated HL using mouse knockout model. Our study will employ contemporary genetic, molecular, cellular, histochemical, and electrophysiological techniques. Proposed work is innovative, as these 4 previously unknown HL genes have been mapped, and we are using combination of mouse and zebrafish model systems to characterize the expression and function of new HL proteins. Also, DFNB100 is a novel HL protein; therefore, its role in the inner ear has never been investigated. The proposed research is significant, first, because it is expected to provide identity of 4 new proteins essential for hearing in humans and also their role in the development, function and maintenance of auditory system in model system. Secondly, provide mechanistic understanding of how DFNB100 is involved in the structural development and/or function of cochlear sensory cells. Third, the proposed study will likely uncover the physiological significance of inositol pyrophosphates metabolism in the cochlear hair cells. Fourth, the knowledge obtained through the proposed studies holds important clinical relevance, with potential to improve the molecular epidemiology, genetic diagnosis and counseling for HL.